A primary function of electronic warfare (EW) systems is to identify radar signal sources. If the EW system is carried aboard a fighter aircraft, for example, the system will listen for radar signals striking the aircraft. It will then attempt to determine the location and movement of the various sources of the radar signals and perhaps identify the source as well. For every object which emits receivable radio waves, the optimal EW system would give the aircraft pilot a complete description of the object.
With the optimal EW system, the pilot would be warned of missiles, aircraft, ground and airborne surveillance systems and a host of other objects, complete with a report of the missile or aircraft type, its location, its trajectory, and more. Unfortunately, the signals received by the aircraft are not sorted according to source, but superimposed over each other or interleaved. A basic requirement of any EW system is that it be capable of deinterleaving the radar signals. In other words, it must be able to group the signals according to their source.
Present EW systems attempt to do this by matching groups of incoming signals to models of various known radar sources, for example, friendly aircraft or dangerous missiles. The groups of signals which do not match any of the models are either discarded or stored for analysis on the ground in much .larger computing systems. This approach has several disadvantages. First, any group of signals which does not match a known model cannot be identified unless and until the aircraft lands. By that time it is too late for the pilot to take evasive action. Second, there is an inherent time delay because a group of signals must be collected before they may be analyzed. If a radar signal source emits only a small number of pulses very quickly, it may not be identified until it disappears.
With the advent of digital radar, the problems with existing deinterleavers become even more acute. While analog radars could generate only a small range of different signals, a digital radar can greatly vary amplitude, frequency, modulation, and many other parameters of its signals with great speed. As a result, a great many more models are required to effectively deinterleave even signals from known sources. With analog radar, one or two models might suffice to identify a specific type of airplane or missile. Once this signal was received and analyzed, it remained a characteristic for that type of source until substantial changes were made to the source's radar hardware. With digital radar, a much larger range of radar signals must be analyzed in order to identify the radar source. It is highly unlikely that the source will display its whole range of capabilities after only a few encounters.